It was for me on the 335i but you will probably have an issue there on your 135i. It might be better to use your 135i shaft and weld the m3 diff flange on. I think Nigelo has the correct flange spare so it might be worth contacting him.

I have already M3 drive shaft + half shaft and diff so I don't need anything else. If my center bearing will not match the M3 drive shaft I will use mine not to make additional holes in car body. + I believe 135 shaft is lighter though maybe not that strong.

BTW if you will be able please add some pics.
Also did you had oem bolts for half shafts and drive shaft to diff?